Historically, dye-type heat-sensitive paper containing a colorless leuco dye and a phenolic acidic substance was developed as a heat-sensitive recording technology by NCR Inc. in the 1960s, and this system has become the mainstream of heat-sensitive recording systems. Thereafter, demand for heat-sensitive paper (hereinafter referred to as “heat-sensitive recording material”) has increased rapidly since (1) miniaturization and price reduction of apparatuses became possible due to development of thermal heads based on semiconductor technologies and significant improvement in cost and performance; (2) increase in quality (higher sensitivity, improvement of head matching property, and the like) of heat-sensitive paper (heat-sensitive recording material) itself was realized; and (3) heat-sensitive recording systems were evaluated to be advantageous in view of user-friendliness, i.e., convenience, low costs, freedom from frequent maintenance, and the like as compared to other recording systems such as static recording, ink jet recording, PPC recording, and the like.
However, as heat-sensitive recording materials are used for facsimile machines, various printers, and the like and have become familiar to daily life, defects of heat-sensitive recording materials have also become well known. Namely, the following defects have been pointed out:                discoloration by light;        discoloration during storage at high temperature (when left in a vehicle, and the like);        fading of a recorded image by chemical agents such as plasticizers in wrapping films, oils, organic solvents in marker pens, ink for ink jet printers, and the like;        a lack of plain paper-like texture (good stamping applicability such as good drying of stamps without bleeding, and the like, a recording surface that is matted and easy to read, good writing property with respect to a pencil, and the like, resistance to stainining due to friction, and the like, and so forth).        
Therefore, development and provision of a heat-sensitive recording material free from the above-mentioned defects and having high value have been demanded.
Recently, heat-sensitive recording materials have been widely used since they are relatively inexpensive and recording apparatuses therefore are compact and do not require frequent maintenance. Under such circumstances, competition in the marketing of heat-sensitive recording materials has become tough, and demand for heat-sensitive recording materials having higher performance that can be differentiated from conventional performance, and specifically heat-sensitive recording materials having high density of developed color, whiteness of background, sharpness, storage stability, good hue and sharpness for a full-color image recorded by an ink jet recording system, or the like has increased. Therefore, intensive investigations regarding various characteristics such as color developing property, storability, and the like of heat-sensitive recording materials are now being conducted in order to satisfy such demands.
The characteristics that heat-sensitive recording materials should have include, for example, (1) high sensitivity (capability to provide high density); (2) high whiteness of a background portion (non-printed portion) (low background fogging property); (3) superior image storability after photographic printing; (4) superior light fastness; (5) superior resistance to chemical substances; (6) sharpness and high image quality; (7) good hue and sharpness of colors for a full-color image recorded by an ink jet recording system; (8) good thermal head matching property and head resistance property by which thermal head abrasion is decreased; (9) plain paper-like feeling; (10) printing applicability that enables printing on a heat-sensitive recording layer, and stamping applicability free from bleeding; (11) applicability for high performance printers such as a high speed printer, and the like; and (12) environment applicability. Under the above-mentioned circumstances, it is demanded that all of these characteristics are simultaneously satisfied without deterioration of any of the characteristics. However, under the present circumstances, a heat-sensitive recording material that can satisfy all of the above-mentioned characteristics simultaneously has not been provided yet.
Conventionally, 2,2-bis(4-hydroxyphenyl)propane (so-called “bisphenol A”) has been widely used as an electron-accepting compound that reacts with an electron-donating colorless dye to develop color used for a heat-sensitive recording material. However, in such a system, a heat-sensitive recording material having satisfactory properties in view of sensitivity, background fogging property, and image storability has not been provided yet.
Furthermore, such a system also has a problem in view of (13) ink jet applicability. Namely, full color information is sometimes recorded on a heat-sensitive recording material using inks for ink jet recording. However, when ink jet recording is carried out on a recording surface of a conventional heat-sensitive recording material containing bisphenol A, hues of inks cannot be reproduced faithfully, sharp hues cannot be obtained, and when an image is already formed on the recording surface by heat-sensitive recording, the image sometimes fades. Furthermore, when the above-mentioned conventional heat-sensitive recording material is placed in contact with a medium having an image recorded by an ink jet printer, background fogging or fading of a recorded image sometimes occurs.